Sidewall image transfer (SIT) is an indirect patterning method that involves the etching of a silicon nitride spacer and a silicon mandrel to achieve sub-lithographic linewidths. Current approaches to etching of a silicon nitride spacer face two main challenges, footing and corner rounding. Current methods used to extract the silicon mandrel involve the redeposition of etch by-products and bombardment by energetic ions. However, these processes result in corner residue and significant damage to the underlying material. New methods are needed that solve these and other problems in sidewall image transfer.